Fanboy’s Lament

One would, as the OP, expect to see significantly more details related to high MP count - whic is not the case...

Yeah, it is. This difference is only 28% in linear pixel count, and we see a commensurate (small) advantage in detail retained. The problem is, people look at pixel counts and expect more than is there because resolution isn't proportional to pixel count, it's proportional to the square root of pixel count. Doubling pixel count only means a 1.4x improvement in theoretical resolution, not 2x.